This invention relates to a tone signal generation device employed in an electronic musical instrument and like devices and, more particularly, to a device capable of generating with a relatively simple construction a tone of a high quality whose tone color changes subtly as time elapses just as in a tone of an acoustic musical instrument.
Known in the art are (1) a device storing a full waveshape from the rising of sounding of a tone to the termination thereof in a waveshape memory and reading out this full waveshape all through and (2) a device storing a tone waveshape for plural periods in a waveshape memory and repeatedly reading out all or part of the stored waveshape. These devices are specifically disclosed in U.S. Pat. No. 4,383,462 or Japanese Preliminary Patent Publication No. 142396/1983. The above U.S. Pat. No. 4,383,462 discloses an electronic musical instrument which aims at producing a tone of a high quality by prestoring a full waveshape from rising to termination of sounding of the tone in a memory and reading out the waveshape therefrom. In the waveshape memory WM31 in FIG. 3 of this U.S. patent, a full waveshape is stored and this full waveshape is read out in response to a signal KD which represents a key depression timing. Such system in which the full waveshape is stored requires a large memory capacity. In order to improve this point, it has been conceived to store a part of waveshape of plural periods out of the complete sounding period in a waveshape memory and obtain a tone signal by repeatedly reading out the partial waveshape. In the above U.S. Pat. No. 4,383,462, an example of such improvement is shown in FIG. 6. A complete waveshape in the attack period is stored in the waveshape memory WM61 and at least one fundamental period of a tone waveshape is stored in the waveshape memory WM62. An attack waveshape is read out from the memory WM61 in response to the key depression (KD signal) and the tone waveshape of the fundamental period is repeatedly read out from the memory WM62 after completion of the readout of the attack waveshape (IMF signal) until the termination of tone generation (DF signal).
The above described prior art tone signal generation devices are disadvantageous in that they require a waveshape memory of a large capacity, particularly so if a tone waveshape signal of a satisfactorily high quality is to be obtained with a high resolution.
It is, therefore, an object of the invention to provide a tone signal generation device capable of generating a tone signal whose tone color (i.e., waveshape) changes with time with a relatively simple construction.